The long-range objective of this work is to explicate the molecular basis of membrane biogenesis and function with particular attention to the role of membrane lipids. We have recently discovered a novel function of acyl carrier protein (ACP), and of apo-ACP, in the enzymic synthesis of the membrane-derived oligosaccharides (MDO) of E. coli. The MDO of E. coli are structural and functional analogs of the cyclic beta, 1-2-glucans of the Rhizobium, thought to be involved in the complex signalling between Rhizobium and specific plant hosts needed for symbiotic nitrogen fixation. Horvath et al. (1986) have reported that the hsnA gene of R. meliloti encodes an inducible acyl carrier protein, the product of which appears to be involved in the signalling process. These developments greatly expand our view of the biological roles of ACP and underscore the urgent need for more information about the metabolism of these proteins both in E. coli and R. meliloti. The proposed work has three major aspects. 1) The metabolism and function of ACP, and of apo-ACP, in E. coli will be further explored. 2) The biochemistry and function of ACP's in R. melitoti will be studied, which should help to answer the challenging question of the function of the hsnA gene product in establishing symbiosis. 3) We will carry out the first detailed study of phospholipid metabolism in Rhizobium, thus filling an important gap in our understanding of the biogenesis and function of membranes in this genus. The significance of the work lies in the fundamental information it will provide on acyl carrier proteins, that play an essential role in lipid metabolism in every kind of living organism, and on symbiotic nitrogen fixation, a process of vast importance for human nutrition and agriculture.